U.S. patent number 8,726,996 [Application Number 12/790,299] was granted by the patent office on 2014-05-20 for device for the focus and control of dynamic underbalance or dynamic overbalance in a wellbore.
This patent grant is currently assigned to Schlumberger Technology Corporation. The grantee listed for this patent is Karim Al Sayed, Carlos E. Baumann, Lawrence A. Behrmann, Adil Mahallab Al Busaidy, Fokko H. C. Doornbosch, Andrew J. Martin, Harvey Williams. Invention is credited to Karim Al Sayed, Carlos E. Baumann, Lawrence A. Behrmann, Adil Mahallab Al Busaidy, Fokko H. C. Doornbosch, Andrew J. Martin, Harvey Williams.
United States Patent |
8,726,996 |
Busaidy , et al. |
May 20, 2014 |
Device for the focus and control of dynamic underbalance or dynamic
overbalance in a wellbore
Abstract
A downhole tool assembly for use in a wellbore includes a
tubular body carrying an explosive which is selectively detonated
to create a dynamic underbalance or overbalance effect in the
wellbore. The tubular body has opposite ends provided with plug
assemblies including plug elements movable between a normally
collapsed state and an actuable expanded state. The plug elements
are adapted to be actuated to the expanded state between the
tubular body and an outer extent of the wellbore before the
creation of the dynamic underbalance or overbalance effect to
isolate a discrete segment of the wellbore to which the dynamic
underbalance or overbalance effect is confined.
Inventors: |
Busaidy; Adil Mahallab Al
(Seeb, OM), Al Sayed; Karim (La Defence Cedex,
FR), Doornbosch; Fokko H. C. (Oegstgeest,
NL), Baumann; Carlos E. (Austin, TX), Behrmann;
Lawrence A. (Houston, TX), Williams; Harvey (Houston,
TX), Martin; Andrew J. (Barton, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Busaidy; Adil Mahallab Al
Al Sayed; Karim
Doornbosch; Fokko H. C.
Baumann; Carlos E.
Behrmann; Lawrence A.
Williams; Harvey
Martin; Andrew J. |
Seeb
La Defence Cedex
Oegstgeest
Austin
Houston
Houston
Barton |
N/A
N/A
N/A
TX
TX
TX
N/A |
OM
FR
NL
US
US
US
GB |
|
|
Assignee: |
Schlumberger Technology
Corporation (Sugar Land, TX)
|
Family
ID: |
43298068 |
Appl.
No.: |
12/790,299 |
Filed: |
May 28, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20110132608 A1 |
Jun 9, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61183102 |
Jun 2, 2009 |
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Current U.S.
Class: |
166/297;
175/4.54; 175/4.52; 166/63; 166/191 |
Current CPC
Class: |
E21B
43/1195 (20130101); E21B 33/1285 (20130101); E21B
33/124 (20130101) |
Current International
Class: |
E21B
43/11 (20060101); E21B 43/00 (20060101); E21B
43/116 (20060101); E21B 29/02 (20060101); E21B
33/12 (20060101) |
Field of
Search: |
;166/297,63,55,55.2,191
;175/4.52,4.54 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
International Search Report & Written Opinion; International
application No. PCT/US2010/036803; Jul. 30, 2010. cited by
applicant.
|
Primary Examiner: Coy; Nicole
Assistant Examiner: Wills, III; Michael
Attorney, Agent or Firm: Peterson; Jeffery R. Clark; Brandon
S.
Parent Case Text
RELATED APPLICATIONS
This application claims the benefit under 35 U.S.C. .sctn.119(e) to
U.S. Non-/Provisional Patent Application Ser. No. 61/183,102,
entitled, "Device for Focus and Control of Dynamic Under Balance
and Dynamic Over Balance in a Borehole," filed on Jun. 2, 2009.
This application is hereby incorporated by reference in its
entirety.
Claims
What is claimed is:
1. A downhole tool assembly for use in a wellbore comprising: a
tubular body carrying an explosive which is selectively detonated
to create a dynamic underbalance or overbalance effect in the
wellbore, the tubular body having opposite ends provided with plug
assemblies including plug elements movable between a normally
collapsed state and an actuable expanded state, wherein each plug
assembly includes an elongated hollow cylinder connected to the
tubular body and an elongated hollow mandrel is connected to and
extends through and beneath the cylinder, wherein the plug elements
are adapted to be actuated to the expanded state between the
tubular body and an outer extent of the wellbore before the
creation of the dynamic underbalance or overbalance effect to
isolate a discrete segment of the wellbore to which the dynamic
underbalance or overbalance effect is confined, wherein further the
plug elements self-deploy to the expanded state upon detonation of
the explosive or other activation of the plug elements, the tubular
body having an internal chamber adapted to be exposed to the
wellbore upon detonation of the explosive or other rupturing of the
tubular body.
2. The downhole tool assembly of claim 1, wherein the mandrel has a
passageway in communication with the internal chamber of the
tubular body.
3. The downhole tool assembly of claim 2, wherein the mandrel has a
vent that permits communication between the passageway and an
interior portion of the cylinder.
4. The downhole tool assembly of claim 2, wherein the explosive is
an elongated detonating cord that is positioned in the passageway
of the mandrel.
5. The downhole tool assembly of claim 1, wherein an elongated
piston is mounted for sliding movement relative to the mandrel and
the cylinder.
6. The downhole tool assembly of claim 5, wherein a spring
surrounds the mandrel and is disposed between the cylinder and the
piston.
7. The downhole tool assembly of claim 5, wherein each plug element
is a flexible, elastomeric element attached between the cylinder
and the piston.
8. The downhole tool assembly of claim 5, wherein each plug element
surrounds the mandrel and the piston.
9. The downhole tool assembly of claim 5, wherein a shear element
is disposed between the mandrel and the piston.
10. The downhole tool assembly of claim 9, wherein the sliding
movement of the piston relative to the mandrel and the cylinder is
normally prevented by the shear element disposed between the
mandrel and the piston.
11. The downhole tool assembly of claim 9, wherein sliding movement
of the piston relative to the mandrel and the cylinder is permitted
upon detonation of the explosive to rupture of the shear
element.
12. The downhole tool assembly of claim 5, wherein each plug
element is movable between the collapsed and expanded states by the
sliding movement of the piston relative to the mandrel and the
cylinder.
13. The downhole tool assembly of claim 5, wherein each plug
element is selectively actuated to the expanded state by squeezing
the plug element between the piston and the cylinder.
14. A downhole tool assembly for use in a wellbore having a series
of perforation tunnels previously formed in a surrounding well
formation and filled with debris, the downhole assembly comprising:
a tubular body positioned in the wellbore adjacent the previously
formed perforation tunnels, the tubular body carrying an explosive
which is selectively actuated to create a dynamic underbalance or
overbalance effect in the wellbore, and having opposite ends
provided with plug assemblies including plug elements movable
between a normally collapsed state and an actuable expanded state,
wherein the plug assemblies are responsive to detonation of the
explosive such that the plug elements are actuated to the expanded
state between the tubular body and an outer extent of the wellbore
to isolate a discrete segment of the wellbore to which purging of
the debris filled perforation tunnels or stimulation of the
wellbore is confined.
15. The downhole tool assembly of claim 14, wherein each plug
element is selectively actuated to the expanded state by squeezing
the plug element between cooperating elements of the plug
assemblies.
16. A method for focusing and containing a dynamic underbalance or
dynamic overbalance effect in a wellbore, the method comprising the
steps of: lowering a downhole tool assembly into a wellbore
adjacent a formation zone of perforation tunnels previously formed
in a formation surrounding the wellbore, the tool assembly carrying
an explosive and having plug assemblies including expandable and
collapsible plug elements provided at opposite ends thereof,
wherein the plug elements are normally in a collapsed state spaced
from an outer extent of the wellbore and are actuable to an
expanded state; activating the plug elements to the expanded state
such that the plug elements extend between the tool assembly and
the outer extent of the wellbore to isolate a discrete segment of
the wellbore from a remainder of the wellbore; detonating the
explosive in the downhole tool assembly to create a dynamic
underbalance or overbalance effect confined to the discrete segment
of the wellbore for purging the perforation tunnels or stimulating
the wellbore, wherein the plug elements are activated in response
to detonation of the explosive; and deactivating the plug elements
to the collapsed state upon termination of the dynamic underbalance
or overbalance effect.
17. The method of claim 16, wherein the plug elements are actuated
to the expanded state by squeezing the plug elements between
cooperating elements of the plug assemblies.
Description
FIELD
The present disclosure generally relates to improving communication
of formation fluids within a wellbore using dynamic underbalance or
dynamic overbalance to effectively manipulate pressure conditions
within a wellbore after perforation tunnels have been previously
formed in the surrounding formation of a well.
BACKGROUND
To complete a well, one or more formation zones adjacent a wellbore
are perforated to allow fluid from the formation zones to flow into
the well for production to the surface or to allow injection fluids
to be applied into the formation zones. A perforating gun string
may be lowered into the wells and the guns fired to create openings
in a casing and to extend perforation tunnels into the surrounding
formation.
The explosive nature of the formation of perforation tunnels
shatters sand grains of the formation. A layer of "shock damaged
region" having a permeability lower than that of the virgin
formation matrix may be formed around each perforation tunnel. The
process may also generate a tunnel full of rock debris mixed in
with the perforator charge debris. The extent of the damage, and
the amount of loose debris in the tunnel, may be dictated by a
variety of factors including formation properties, explosive charge
properties, pressure conditions, fluid properties and so forth. The
shock damaged region and loose debris in the perforation tunnels
may impair the productivity of production wells or the injectivity
of injector wells.
To address these issues, pressure in a wellbore interval is
manipulated in relation to the reservoir or surrounding formation
pore pressure to achieve removal of debris from perforation
tunnels. The pressure manipulation includes creating a transient
underbalance condition (the wellbore pressure being lower than a
formation pore pressure) prior to detonation of a detonation cord
or shaped charges of limited energy. Pressure manipulation also
includes creating an overbalance pressure condition (when the
wellbore pressure is higher than the formation pore pressure) prior
to detonation or explosion of shaped charges of a perforating gun
or a propellant. Creation of an underbalance condition can be
accomplished in a number of different ways, such as by use of a low
pressure chamber that is opened to create the transient
underbalance condition, the use of empty space in a perforating gun
or tube to draw pressure into the gun right after firing of shaped
charges, and other techniques. The underbalanced condition results
in a suction force that will extract debris out of the perforation
tunnels and fluid from the wellbore into the tube enabling the well
to flow more effectively or more efficient injection of fluids into
the surrounding formation. Creation of an overbalance condition can
be accomplished by use of a propellant (which when detonated causes
high pressure gas buildup), a pressurized chamber, or other
techniques. The burning of the propellant can cause pressure to
increase to a sufficiently high level to fracture the formation.
The fracturing allows for better communication of reservoir fluids
from the formation into the wellbore or the injection of fluids
into the surrounding formation.
The manipulation of wellbore pressure conditions causes at least
one of the following to be performed: (1) enhance transport of
debris (such as sand, rock particles, etc.) from perforation
tunnels; (2) achieve near-wellbore stimulation; and (3) perform
fracturing of surrounding formation.
During the manipulation of pressure, one or more packers or plugs
are known to be positioned between the inside of the wellbore and
the outside of the perforating gun or tube to isolate the interval
over which the detonation or explosion takes place to achieve a
quicker and amplified response for the underbalance or overbalance
effect.
It remains desirable to provide a device for confining the effects
of a dynamic underbalance or dynamic overbalance in a defined
region of the wellbore to enable removal of debris from the
perforation tunnels and/or stimulation within the well.
SUMMARY
The present application discloses a downhole tool assembly defining
a transient plug arrangement which improves communication of
formation fluids in the wellbore. In one example, a downhole tool
assembly for use in a wellbore includes a tubular body carrying an
explosive which is selectively detonated to create a dynamic
underbalance or overbalance effect in the wellbore. The tubular
body has opposite ends provided with plug assemblies including plug
elements movable between a normally collapsed state and an actuable
expanded state. The plug elements are adapted to be actuated to the
expanded state between the tubular body and an outer extent of the
wellbore before the creation of the dynamic underbalance or
overbalance effect to isolate a discrete segment of the wellbore to
which the dynamic underbalance or overbalance effect is
confined.
In the particular example disclosed, the plug assemblies are
responsive to detonation of the explosive such that the plug
elements are actuated to the expanded state between the tubular
body and an outer extent of the wellbore to isolate the discrete
segment of the wellbore to which purging of the debris filled
perforation tunnels or stimulation of wellbore is concentrated. In
an alternative method, the plug assemblies could be actuated by an
electrical, hydraulic or mechanical command.
The present disclosure further contemplates an exemplary method for
forming and controlling a dynamic underbalance or dynamic
overbalance effect on a wellbore wherein the method includes the
steps of (1) lowering a downhole tool assembly into a wellbore
adjacent a formation zone of perforation tunnels previously formed
in a formation surrounding the wellbore, the tool assembly carrying
an explosive and having plug assemblies including expandable and
collapsible plug elements provided at opposite ends thereof wherein
the plug elements are normally in a collapsed state spaced from an
outer extent of the wellbore and are actuable to an expanded state;
(2) activating the plug elements to the expanded state such that
the plug elements extend between the downhole tool assembly and the
outer extent of the wellbore to isolate a discrete segment of the
wellbore from a remainder of the wellbore; (3) detonating the
explosive in the downhole tool assembly to create a dynamic
underbalance or overbalance effect confined to the discrete segment
of the wellbore for purging the perforation tunnels or stimulating
the wellbores; and (4) deactivating the plug elements to the
collapsed state upon termination of the dynamic underbalance or
overbalance effect.
BRIEF DESCRIPTION OF THE DRAWINGS
The best mode is described herein below with reference to the
following drawing figures.
FIG. 1 is a sectional view of a well formation having a wellbore
provided with a downhole tool assembly according to the present
disclosure;
FIG. 2 is an enlarged fragmentary sectional view of a lower portion
of FIG. 1 in an unfired condition with certain portions of the
structure surrounding the wellbore being omitted for
simplicity;
FIG. 3 is an enlarged fragmentary sectional view similar to FIG. 2
showing the downhole tool assembly during a fired condition;
FIG. 4 is a representation of the downhole tool assembly of FIG.
1;
FIG. 5 is a representation of the downhole tool assembly of FIG. 3;
and
FIG. 6 is a further representation of the downhole tool assembly
following a fired condition.
DETAILED DESCRIPTION
In the following description, certain terms have been used for
brevity, clearness and understanding. No unnecessary limitations
are to be implied therefrom beyond the requirement of prior art
because such terms are used for descriptive purposes and are
intended to be broadly construed. The different configurations and
methods described herein may be used alone or in combination with
other configurations, systems and methods. It is to be expected
that various equivalents, alternatives and modifications are
possible within the scope of the appended claims.
Referring now to the drawings, FIG. 1 illustrates a typical well
installation 10 including a wellbore 12 normally containing
borehole fluid 14. As is well known, the wellbore 12 has a
surrounding casing 16 and cement 18 disposed between the casing 16
and the surrounding surface formation 20. A wellhead 22 is
positioned at the top of the surface formation 20, and is provided
with an open bottom tubing 24 that extends downwardly into an upper
portion of the wellbore 12. In the well installation 10
illustrated, the surface formation 20 includes an area of caprock
26, a damaged formation 28 and an undamaged formation 30, all of
which surround cement 18. Perforation tunnels 32 extend through the
casing 16 and cement 18 into the damage formation 28 at one or more
desired formation zones 33.
The perforation tunnels 32 are previously formed using a
perforating gun string to allow fluid flow from the formation zones
33 to flow into the well for production to the surface, or to allow
stimulating injection fluids to be applied to the formation zones.
The explosive nature of the formation of the perforation tunnels 32
shatters the sand grains in the damaged formation 28 and typically
generates tunnels 32 full of rock debris mixed in with perforator
charge debris. Such debris is known to impair the productivity of
production wells and negatively impact upon the flow of formation
fluids in the well. The present disclosure sets forth a device
provided with a transient plug arrangement which is used to clean
the debris from the plug perforation tunnels 32 or otherwise
stimulate the surface formation 20 by focusing and controlling a
dynamic underbalance or dynamic overbalance condition in a desired
formation zone 33 so as to improve fluid communication in this zone
33 of the well.
In accordance with the present disclosure, a downhole tool assembly
34 is lowered into the wellbore 12 in a zone of previously formed
perforation tunnels 32. The tool assembly is suspended in the
wellbore 12 by a carrier structure such as by a cable 36 that
extends through the wellhead 22. The lower end of cable 36 is
secured to a head 38 which, in turn, is connected to a casing
collar locator 40 and a firing head 42. A downhole tool 44 in the
form of an elongated hollow gun or tube has an upper end that is
connected to the firing head 42, and a lower head attached to a
connector 46 with a threaded end plug 48. The downhole tool
assembly 34 includes an upper plug assembly 50 positioned above and
in communication with the downhole tool 44, and a lower plug
assembly 52 inverted with respect to, and similar in construction
to plug assembly 50 and positioned below and in communication with
the downhole tool assembly 44. Because of the similarity and
construction of the upper plug assembly 50 and the lower plug
assembly 52, only the description of the lower plug assembly 52 is
set forth hereafter.
FIG. 2 shows the downhole tool assembly 34 in an installed or
unfired condition, while FIG. 3 illustrates the downhole tool
assembly 34 during a fired condition.
FIGS. 1-6 depict the downhole tool assembly 34 as used to focus and
control the effects of dynamic underbalance in a chosen area of the
wellbore 12. However, as will be understood hereafter, the downhole
tool assembly 34 may also be employed to isolate the effects of
dynamic overbalance, if desired.
Referring now to FIGS. 1-3, the downhole tool 44 has an elongated
tubular body 54 which is generally cylindrical in cross section. It
can be appreciated from FIG. 1, that downhole tool 44 as well as
head 38, casing collar locator 40, firing head 42, the upper and
lower plug assemblies 50, 52 and the connector 46 all have
substantially similar cylindrical shape and outer diameters which
will permit the insertion and extraction of assembly 34 relative to
wellbore 12. The tubular body 54, when positioned in the downhole
tool assembly 34, defines a sealed internal underbalance chamber 56
(FIGS. 2 and 3) which typically contains only air at atmospheric
pressure such as that set at the well surface for insertion into
the wellbore 12. Air at atmospheric pressure provides an internal
chamber pressure which is significantly less than the wellbore
pressure encountered at a formation zone 33 or the formation pore
pressure.
As seen in FIG. 2, the tubular body 54 has a trunk 58 which is
threadedly connected to an upper end 60 of elongated hollow
cylinder 62 that extends from the body 54. An elongated hollow
piston 64 is disposed for sliding movement back and forth inside
the cylinder 62. The piston 64 has an enlarged upper end 66 that
normally is positioned against a lower end 68 of the cylinder 62
when the assembly 34 is in the unfired condition in the wellbore
12. A pair of annular O-rings or seals 70 is provided between the
inner surface of cylinder 62 and the outer surface of the piston
upper end 66. A lower end 72 of the piston 64 is formed with a
central recess 74, and is normally disposed upon the top of
connector 46 when the assembly 34 is in the unfired condition.
The piston 64 slides back and forth upon an elongated hollow
mandrel 76 that has a top end 78 threadably secured to a neck
portion 80 of a cylinder 62 such that the mandrel 76 extends
through the center of the cylinder 62 and lies inwardly of the
piston 64. As seen from FIG. 3, a lower end 82 of the mandrel 76 is
threadably attached to the connector 46. The mandrel 76 is formed
with a vertically extending passageway 84 (FIG. 3) which opens into
tubular body 54, and is designed to hold a detonating or primer
cord 86 that extends between the firing head 42 and the lower end
72 of piston 64 when assembly 34 is in the unfired condition. If a
non-explosive device is required, the passageway 84 would contain
electrical connections leading to an electrical release system.
An upper portion of mandrel 76 is constructed with a vent 88 that
communicates with an interior of cylinder 62. A lower end 90 of the
mandrel 76 is provided with an opening 92 for retaining a rupture
element, electrical release or shear disk 94 that normally extends
radially into the piston recess 74 when the assembly 34 is in the
unfired condition. An annular O-ring or seal 96 is provided between
the lower end 90 of mandrel 76 and the lower end 72 of piston 64. A
coil spring 98 surrounds the mandrel 76 and lies inwardly of the
inner surface of cylinder 62. The spring has a top end 100 engaged
against the neck portion 80 of the cylinder 62, and a bottom end
102 engaged against the upper end 66 of piston 64.
The lower plug assembly 52 (as well as the upper plug assembly 50)
typically includes a flexible, elastomeric production packer or
plug element 104 which is expandable and collapsible. The plug
element 104 is generally designed to be temperature, chemical and
tear resistant as well as extremely elastic. As seen in FIG. 2, the
plug element 104 surrounds the piston 64 and extends between the
cylinder 62 and the piston 64. More particularly, a top end 106 of
the plug element 104 is attached to a recessed portion at the lower
end 68 of cylinder 62. A bottom end 108 of the plug element 104 is
secured to a recessed portion at the lower end 72 of piston 64. In
the example shown, the plug element 104 has an inner layer 110 and
an outer layer 112.
As will be explained in greater detail below, the foregoing
construction generally provides that each plug element 104 is
movable between collapsed and expanded states or positions relative
to the inside of casing 16 by virtue of sliding movement of piston
64 relative to the cylinder 62 and the mandrel 76.
The operation of the downhole tool assembly 34 of the present
disclosure will now be described, with initial reference to FIGS. 1
and 4 which show the tool 44 suspended in the wellbore 12
containing borehole fluid 14 and positioned adjacent a formation
zone 33 having a series of previously formed perforation tunnels 32
filled with damage and debris. The tool 44 is in the installed or
unfired condition as described above with internal chamber 56 (FIG.
1) of the tool 44 being at atmospheric pressure which is
significantly lower than the pressure in the surrounding wellbore
12 and the pore pressure of surrounding formation 20. The lower
pressure in internal chamber 56 is in communication with the top of
each piston 64 via the mandrel passageway 84 and the vent 88. Each
piston 64 is prevented from slidably moving along its mandrel 76
towards the low pressure in chamber 56 by the engagement of the
ruptured disk 94 in the mandrel 76 and, to some extent, by the
spring 98 which is normally biased against the top of piston
64.
When it is desired to focus an underbalance event in a desired
formation zone 33, a well operator actuates the firing head 42 and
detonates the primer cord 86 causing an extremely rapid explosion
along the entire length thereof. The firing of primer cord 86
causes rupturing 112 of the tubular body 54, as shown in FIG. 5,
and also ruptures the shear disks 94 which frees the pistons 64 to
slide along the mandrels 76. Rupturing the tubular body 54 creates
a pressure differential between the higher pressure in wellbore 12
and the lower pressure in the internal chamber 56. This causes the
pistons 64 to move quickly along mandrels 76 towards each other in
the direction of arrows A shown in FIG. 5 against the relatively
weak force of springs 98 which are compressed. At the same time,
flexible plug elements 104 are rapidly squeezed or compressed
adjacent the ends 68 of the cylinders 62 (FIG. 3) so as to
instantaneously deploy and expand the plug elements 104 into
temporary plugging engagement with the inside of casing 16. The
existing pressure forces maintain the pistons 64 and plug elements
104 in position.
Upon instantaneous deployment of the plug elements 104, a dynamic
underbalance effect created by the pressure differential is
initiated resulting in a suction flow of the fluid from the
wellbore 12 and debris from the perforation tunnels 32 only from
the isolated wellbore zone 114 (FIG. 5) defined by and between the
expanded plug elements 104. In the meantime, the low pressure sides
of the pistons 64 are flooded with borehole fluid 14 which flows
through the exposed ruptured openings 116 (FIG. 3) and the
passageways 84 in mandrels 76 equalizing the pressure and allowing
the plug elements 104 to turn to their original collapsed shape and
dimensions. The equalized pressure also allows the compressed
springs 98 to assist in returning the plug elements 104 to their
original shape as shown in FIG. 6. Upon restoration of the plug
elements 104 to their initial condition, the tool 44 filled with
fluid and debris is extracted from wellbore 12 such that the
cleaned material deposited in the tubular body 54 may be analyzed,
if desired. Thereafter, the fractured tool 44 including the plug
elements 104 may be disposed of.
It should be understood from the above exemplary embodiment that
the downhole tool assembly 34 creates a transient mechanical plug
arrangement that is utilized to focus and control the effect of
dynamic underbalance in the wellbore zone 114 temporarily defined
by the expanded plug elements 104. Such arrangement disrupts the
movement and pressure effects of the borehole fluids outside the
wellbore zone 114 towards the area of dynamic underbalance so as to
maximize the effect of cleaning of debris from the perforation
tunnels 32 in the zone 114. In addition, the transient plug
arrangement confines the effect of the explosion occurring in the
tubular body 54 to the defined wellbore zone 114.
While the exemplary embodiment set forth above is described for a
dynamic underbalance effect, it should be appreciated that the
present disclosure can also be used to focus and control the
effects of dynamic overbalance, if desired. In such case, plug
elements 104 would again be positioned above and below a dynamic
overbalance chamber defined by tool 44, and tubes having low
pressure chambers would be positioned above and below plug elements
104.
In the present disclosure, the plug elements 104 are self-deployed
by the pressure differential created by the detonation before the
transient pressure event (dynamic underbalance or dynamic
overbalance) occurs. However, it should be realized that the plug
deployment may be independent of the event that causes the
underbalance or overbalance condition. That is, it is not essential
that the plug deployment be triggered by the primer cord explosion.
Plug deployment, as well as rupturing of the tubular body 54, could
otherwise be actuated, such as, for example, by an electrical
solenoid or other electromechanical or hydraulic device before the
underbalance or overbalance effect takes place.
This written description uses examples to disclose the invention,
including the best mode, and also to enable any person skilled in
the art to make and use the invention. The patentable scope of the
invention is defined by the claims, and may include other examples
that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have
structural elements that do not differ from the literal language of
the claims, or if they include equivalent structural elements with
insubstantial differences from the literal languages of the
claims.
Various alternatives and embodiments are contemplated as being with
in the scope of the following claims, particularly pointing out and
distinctly claiming the subject matter regarded as the
invention.
* * * * *